Infectious bursal disease, also known as Gumboro disease, infects poultry world-wide and is responsible for many losses in the poultry industry. Infectious bursal disease is known to be caused by a virus, the infectious bursal disease virus (IBDV). This disease often affects poultry as young as one to six weeks old and causes inflammation, diarrhea, muscular hemorrhaging, bleeding, damage to the immune system and necrosis of the Bursa of Fabricii.
The immunosuppression results from a depletion of the chicken's B lymphocytes (Burkhardt E., Muller H. (1987) Susceptibility of chicken blood lymphocytes and monocytes to infectious bursal disease virus (IBDV). Arch Virol 94:297-303). Secondary infections are commonly associated with infectious bursal disease (Cervantes H. M., Munger L. L., Ley D. H., Ficken M. D. (1988) Staphylococcus-induced gangrenous dermatitis in broilers. Avian Dis 32:140-142; Hofacre C. L., French J. D., Fletcher O. J. (1986) Subcutaneous clostridial infection in broilers. Avian Dis 30:620-622; Rosenberger J. K., Gelb Jr. J (1977) Response to several avian respiratory viruses as affected by infectious bursal disease virus. Avian Dis 22:95-105; Rosenberger J. K., Klopp S., Eckroade R. J., Krauss W. C. (1975) The role of the infectious bursal agent and several avian adenoviruses in the hemorrhagic-aplastic-anemia syndrome and gangrenous dermatitis. Avian Dis 19:717-729; Wyeth P. J. (1975) Effect of infectious bursal disease on the response of chickens to s typhimurium and E coli infections. Vet Rec 96:238-243). The IBDV virion consists of two segments of double-stranded RNA (Muller H., Scholtissek C., Becht H. (1979) The genome of infectious bursal disease virus consists of two segments of double-stranded RNA. J Virol 31:584-589). One segment, called segment A, encodes a fusion protein which is cleaved into the structural proteins VP2, VP3 and VP4 (Hudson P. J., McKern N. M., Power B. E., Azad A. A. (1986) Genomic structure of the large RNA segment of infectious bursal disease virus. Nucleic Acid Res 14:5001-5012). The other segment, segment B, encodes the putative viral polymerase VP1 (Morgan M. M., Macreadie I. G., Harley V. R., Hudson P. J., Azad A. A. (1988) Sequence of the small double-stranded RNA genomic segment of infectious bursal disease virus and its deduced 90-kDa product. Virol 240-242). A neutralizing monoclonal antibody (MAb) binding site was mapped to a region of VP2 between amino acids 206 and 350 (Azad A. A., Jagadish M. N., Fahey K. J. (1987) Deletion mapping and expression in Escherichia coli of the large genomic segment of a birnavirus. Virol 161:145-152). Analysis of the nucleic acid and predicted amino acid sequences among several strains of IBDV has revealed an area of high variability among strains of IBDV within this region (amino acids 239-332) (Bayliss C. D., Spies K., Peters R. W., Papageorgiou A., Muller H., Boursnell M. E. G. (1990) A comparison of the sequences of segment A of four infectious bursal disease virus strains and identification of a variable region in VP2. J Gen Virol 71:1303-1312).
Several expression systems have been utilized to produce the IBVD VP2 protein. Azad et al. (Azad A., Macreadie I., Vaughan P., Jagadish M., McKern N., Heine H. G., Failla P., Ward C. (1990) Full protection against an immunodepressive viral disease by a recombinant antigen produced in yeast. Vacc 90:59-62) expressed VP2 as a fused and non-fused protein in Escherichia coil. Both expression products were poor immunogens. A recombinant fowlpox virus expressing VP2 protected birds challenged with IBDV against mortality, but not against damage to the bursa (Bayliss C. D., Peters R. W., Cook J. K. A., Reece R. L., Howes K., Binns M. M., Boursnell M. E. G. (1991) A recombinant fowlpox virus that expresses the VP2 antigen of infectious bursal disease virus induces protection against mortality caused by the virus. Arch Virol 120:193-205). A recombinant VP2 protein produced in yeast induced neutralizing antibodies and protected progeny chickens from IBDV challenge (Hofacre et al., 1986, supra). IBDV antigen could not be detected in the bursa of progeny from birds immunized with the recombinant yeast protein following challenge with the virus. Recombinant proteins expressed in baculovirus have been produced in amounts of 1 to 500 mg/ml (Luckow V. A., Summers M. D. (1988) Trends in the development of baculovirus expression vectors. Biotech 6:47-56; Smith G. E., Summers M. D., Fraser M. J. (1983) Production of human beta interferon in insect cells infected with a baculovirus expression vector. Mal Cell Biol 3:2156-2165). This expression system utilizes many of the protein modification, processing and transport systems that occur in higher eukaryotic species.
Immunologic studies involving IBDV have suggested that VP2 contains a conformational dependent neutralizing epitope which could be used to distinguish serotypes (Becht, H., Muller H. K. (1988) Comparative studies on structural and antigenic properties of two serotypes of infectious bursal disease virus. J Gen Virol 69:631-40). A monoclonal antibody (1/A6) against VP2 has been mapped to a small highly variable region (Azad et al., 1987, supra).
IBDV proteins have also been expressed using baculovirus (Vakharia V. N., Snyder D. B., He J., Edwards G. H., Savage P. K., Mengel-Whereat S. A. (1993) Infectious bursal disease virus structural proteins expressed in a baculovirus recombinant confer protection in chickens. J Gen Virol 74:1201-1206), wherein it was reported that these proteins reacted with IBDV specific monoclonal antibodies and resembled the native viral proteins. Seventy-nine percent of the birds vaccinated using these baculovirus expressed VP2, VP3 and VP4 proteins were protected against a homologous IBDV challenge.
In addition, other vaccines have been produced in an attempt to control infectious bursal disease. These vaccines, developed containing either live or attenuated viruses, or cultures of the bursal cells for example, while protecting the poultry from mortality, still cause symptoms of infectious bursal disease in the vaccinated poultry. These symptoms included growth retardation and injury to the Bursa of Fabricii. Another problem with the prior art vaccines is that there are increasing outbreaks of infectious bursal disease which are not prevented from occurrence by any of the prior art vaccines, Another problem is the immunization itself of the poultry. Both the timing and method of administration of the vaccine continue to present problems. In particular, problems arise with attempts to vaccinate newly hatched poultry since such newly hatched poultry are often hatched with maternal antibodies to the infectious bursal disease (either to previous infections or vaccination of the hen against the infectious bursal disease). Thus, the time period for vaccination becomes critical. It is important to effectively and rapidly vaccinate large numbers of poultry. The mass immunization of poultry is best effected through such methods of spraying or in the drinking water of the poultry.
Therefore, there are still problems in the prior art to determine the causes of new outbreaks of infectious bursal disease and to develop a vaccine which is resistant to both the known strains and further strains of infectious bursal disease. There is a further need to determine a method of preventing such further outbreaks through vaccination of the affected population. There is a further need to develop a vaccine which can be administered in a timely manner, both by achieving vaccination at the critical times in the poultry's life and by mass immunization to rapidly inoculate the entire poultry population. There is still a further need to provide a vaccine which does not cause symptoms of infectious bursal disease to occur in the vaccinated poultry.